MEASUREMENTS OF GATE VOLTAGE-DEPENDENCE OF ELECTRON-MOBILITY IN DELTA-DOPED HFETS

We report the results of the measurements of the gate voltage dependen ce of the electron mobility in Heterostructure Field Effect Transistor s (HFET's) using a spilt C-V technique. This method allows us to deduc e this dependence without making any assumptions about other parameter s such as the threshold voltage. The dependence of the electron mobili ty in the HFET channel on the gate voltage depends on the heterointerf ace quality. In some samples, the mobility increases with the increase of the gate voltage. In other samples (grown on a different Molecular Beam Epitaxy machine), the mobility drops to nearly a half of its max imum value at high gate voltages. This means that, in these samples, t he electron mobility is strongly dependent on the transverse electric field (similar to an analogous behavior in p- and n-channel MOSFET's).